Lernaean Hydra Picture

So poisonous it's footprints were deadly, and having the ability to regrow two heads for every one destroyed (although one was immortal), the Hydra was a formidable monster that lived in the swamp near Lernae. To make matters worse for any would-be monster slayers, the Hydra had an ally, a giant crab.

Despite being seemingly impossible, Hercules and his nephew Iolaos were able to slay the monsters (and safely buried the immortal Hydra head under a rock). Although unable to kill the heroes, Hera rewarded the Hydra and Crab for their efforts by placing them in the heavens as the constellations Hydra and Cancer.